ODBC (Open Database Connectivity)
is an abstract API which allows you to
write applications which can interoperate with various RDBMS servers. ODBC
provides a product-neutral interface between frontend applications
and database servers, allowing a user or developer to write
applications which are transportable between servers from different
manufacturers..

The ODBCAPI matches up on the backend to an ODBC-compatible data source. This could be
anything from a text file to an Oracle or PostgresRDBMS.

The backend access come from ODBC
drivers, or vendor specifc drivers that allow data access.
psqlODBC is such a driver, along
with others that are available, such as the OpenLink ODBC drivers.

Once you write an ODBC application,
you should be able to connect to any back end database, regardless of the vendor, as
long as the database schema is the same.

For example. you could have MS SQL
Server and Postgres servers
which have exactly the same data. Using ODBC, your Windows application would make exactly
the same calls and the back end data source would look the same (to
the Windows app).